Systems and methods for forming nanowires using anodic oxidation

ABSTRACT

Structures, devices and methods are provided for forming nanowires on a substrate. A first protruding structure is formed on a substrate. The first protruding structure is placed in an electrolytic solution. Anodic oxidation is performed using the substrate as part of an anode electrode. One or more nanowires are formed in the protruding structure. The nanowires are surrounded by a first dielectric material formed during the anodic oxidation.

PRIORITY CLAIM AND CROSS-REFERENCE

This disclosure claims priority to and benefit from U.S. ProvisionalPatent Application No. 61/972,462, filed on Mar. 31, 2014, the entiretyof which is incorporated herein by reference.

BACKGROUND

The technology described in this disclosure relates generally tosemiconductor devices and more particularly to fabrication ofsemiconductor devices.

Anodic oxidation includes an accelerated electrochemical oxidationprocess. For example, a cathode electrode and an anode electrode areimmersed in an electrolytic solution and connected electrically to apower supply. Oxides can be grown at the anode electrode at roomtemperature. Depending on process conditions, the anodic oxide may berelatively porous. An annealing process can be performed at atemperature in a range of about 450° C. to about 500° C. to densify theoxide and remove residual water.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 depicts an example diagram showing a top view of an apparatus foranodic oxidation for forming nanowires, in accordance with someembodiments.

FIG. 2 depicts an example diagram showing a side view of the apparatusas shown in FIG. 1, in accordance with some embodiments.

FIG. 3 depicts an example diagram showing an anode electrode as part ofthe apparatus as shown in FIG. 1, in accordance with some embodiments.

FIG. 4 depicts another example diagram showing an anode electrode aspart of the apparatus as shown in FIG. 1, in accordance with someembodiments.

FIG. 5 depicts an example diagram showing protruding structures on awafer electrode, in accordance with some embodiments.

FIG. 6 depicts an example diagram showing patterns for formingprotruding structures on a wafer electrode, in accordance with someembodiments.

FIG. 7(A)-FIG. 7(C) depict example diagrams of an anodic oxidationprocess performed on a protruding structure showing charge distribution,in accordance with some embodiments.

FIG. 8(A)-FIG. 8(C) depict example diagrams of an anodic oxidationprocess performed on a protruding structure without showing chargedistribution, in accordance with some embodiments.

FIG. 9(A)-FIG. 9(D) depict example diagrams showing anodic oxidationperformed on different wafer electrodes, in accordance with someembodiments.

FIG. 10(A) depicts an example diagram showing a pattern of a protrudingstructure on a wafer electrode, and FIG. 10(B) depicts an examplediagram showing a cross-section view of the pattern along a cutline, inaccordance with some embodiments.

FIG. 11 depicts an example diagram showing a cross-section view of awafer electrode including a protruding structure after anodic oxidation,in accordance with some embodiments.

FIG. 12(A) and FIG. 12(B) depict example diagrams showing formation ofmultiple nanowires through anodic oxidation, in accordance with someembodiments.

FIG. 13(A)-FIG. 13(C) depict other example diagrams showing formation ofmultiple nanowires through anodic oxidation, in accordance with someembodiments.

FIG. 14(A)-FIG. 14(C) depict other example diagrams showing formation ofmultiple nanowires through anodic oxidation, in accordance with someembodiments.

FIG. 15 depicts an example diagram showing anodic oxidation for multiplewafer electrodes, in accordance with some embodiments.

FIG. 16 depicts an example diagram showing a top view of an originalmask for forming a protruding structure for a transistor structure, inaccordance with some embodiments.

FIG. 17(A)-FIG. 17(C) depict example diagrams showing cross-sectionviews along different cutlines respectively, in accordance with someembodiments.

FIG. 18(A)-FIG. 18(D) depict example diagrams showing a process forfabricating a transistor structure using nanowires formed through anodicoxidation, in accordance with some embodiments.

FIG. 19(A)-FIG. 19(D) depict other example diagrams showing a processfor fabricating a transistor structure using nanowires formed throughanodic oxidation, in accordance with some embodiments.

FIG. 20 depicts an example diagram showing a nanowire device, inaccordance with some embodiments.

FIG. 21 depicts an example flow chart for forming nanowires, inaccordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “on,” “in,” “under,” “top,”“bottom” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. The spatially relative termsare intended to encompass different orientations of the device in use oroperation in addition to the orientation depicted in the figures. Theapparatus may be otherwise oriented (rotated 90 degrees or at otherorientations) and the spatially relative descriptors used herein maylikewise be interpreted accordingly.

FIG. 1 depicts an example diagram showing a top view of an apparatus foranodic oxidation for forming nanowires, in accordance with someembodiments. As shown in FIG. 1, in the apparatus 100, a cathodeelectrode 102 including metal materials (e.g., Ag, Pt, etc.) and ananode electrode 104 including a semiconductor wafer (e.g., Si, GaAs,semiconductor-on-insulator, III-V materials, II-VI materials, etc.) areplaced (e.g., immersed) in an electrolytic solution 106 for anodicoxidation. The cathode electrode 102 and the anode electrode 104 areconnected electrically to a power supply 108. An electrode holder 110includes multiple slots 112 for holding the cathode electrode 102 andthe anode electrode 104. The apparatus 100 further includes a tank 114to contain the electrolytic solution 106.

FIG. 2 depicts an example diagram showing a side view of the apparatusas shown in FIG. 1, in accordance with some embodiments. As shown inFIG. 2, the anode electrode 104 includes a wafer electrode 202 and aconductive material 204 (e.g., Pt, Ag, inert conductive materials,etc.), where the wafer electrode 202 includes a semiconductor wafer(e.g., Si, GaAs, semiconductor-on-insulator, III-V materials, II-VImaterials, etc.). One or more protruding structures 208 are formed onthe wafer electrode 202 for nanowire formation.

Specifically, the electrolytic solution 106 includes deionized water.For example, one or more chemicals may be included in the electrolyticsolution 106 to provide a suitable PH level and/or suitable ionicstrength. The power supply 108 includes a direct-current power supplywith or without alternating-current components (e.g., 1 MHz). Aninsulator material 206 includes a rubber, O-ring, or any otherinsulating material for support of the metal electrode 204.

FIG. 3 depicts an example diagram showing an anode electrode as part ofthe apparatus as shown in FIG. 1, in accordance with some embodiments.As shown in FIG. 3, the conductive material 204 (e.g., Pt, Ag, inertconductive materials, etc.) corresponds to a conductive holder thatholds the wafer electrode 202 so that the wafer electrode 202 does notmove around freely.

Specifically, the conductive material 204 includes a top part 302 and abottom part 304 for holding the wafer electrode 202. The top part 302 isin contact with part of a top surface of the wafer electrode 202 andincludes holes for clamping the wafer electrode 202. The protrudingstructures 208 are not in contact with the conductive material 204. Thebottom part 304 is in contact with a bottom surface of the waferelectrode 202.

In some embodiments, the wafer electrode 202 is sandwiched between thetop part 302 and the bottom part 304 of the conductive material 204through vacuum. The wafer electrode 202 and the conductive material 204are electrically connected to the power supply 108 through one or morewires attached to the conductive material 204. The protruding structure208 has a width and a height, and an aspect ratio of the protrudingstructure 208 is equal to the height divided by the width. In certainembodiments, the aspect ratio of the protruding structure 208 is largerthan an aspect-ratio threshold (e.g., 1).

FIG. 4 depicts another example diagram showing an anode electrode aspart of the apparatus as shown in FIG. 1, in accordance with someembodiments. As shown in FIG. 4, the conductive material 204 includes aconductive holder 406 and a metal electrode 408. The conductive holder406 holds both the wafer electrode 202 and the metal electrode 408.

Specifically, the conductive holder 406 includes a top part 402 and abottom part 404 for holding both the wafer electrode 202 and the metalelectrode 408. The top part 402 is in contact with part of a top surfaceof the wafer electrode 202 and includes holes for clamping the waferelectrode 202 and/or the metal electrode 408. The protruding structures208 are not in contact with the conductive holder 406. The bottom part404 is in contact with a bottom surface of the metal electrode 408.

In some embodiments, the metal electrode 408 includes Ag, Pt, inertconductive materials, etc. The wafer electrode 202 and the metalelectrode 408 are sandwiched between the top part 402 and the bottompart 404 of the conductive holder 406 through vacuum. The waferelectrode 202, the metal electrode 408, and the conductive holder 406are electrically connected to the power supply 108 through one or morewires attached to the conductive holder 406.

FIG. 5 depicts an example diagram showing protruding structures on awafer electrode, in accordance with some embodiments. As shown in FIG.5, the protruding structures 208 include nanowire-shaped structures,nanoslates, nanorods, nanostructures disposed between pads, or any othersuitable nanostructures. The aspect ratios of the protruding structures208 are greater than a threshold (e.g., 1).

For example, a minimum feature width is in a range of about 10 nm toabout 100 nm. The heights of the protruding structures 208 are in arange of about 10 nm to about 500 nm, depending on the number ofnanowires needed. The side walls of the protruding structures 208 areof: vertical shapes, trapezoidal shapes, scalloped shapes, shapes ofwhich a top width is larger than or equal to a bottom width, or anyother suitable shapes. The conductive material 204 (e.g., a top part)includes holes 504 for clamping the wafer electrode 202. The waferelectrode 202 and the conductive material 204 are electrically connectedto the power supply 108 through one or more wires 502 attached to theconductive material 204.

FIG. 6 depicts an example diagram showing patterns for formingprotruding structures on a wafer electrode, in accordance with someembodiments. As shown in FIG. 6, the patterns 602 are used to formprotruding structures (e.g., the structures 208) on a substrate. In someembodiments, the patterns 602 are formed using photoresist, oxides,silicon nitrides, or any other suitable materials.

A trench etching is performed using the patterns 602 as etch masks toform the protruding structures (e.g., the structures 208) with highaspect ratios. In certain embodiments, the trench etching includesrepeated isotropic etching cycles, an anisotropic etching, or a combinedisotropic/passivation cycles. The substrate including the protrudingstructures is then placed (e.g., immersed) in an electrolytic solutionfor anodic oxidation.

FIG. 7(A)-FIG. 7(C) depict example diagrams of an anodic oxidationprocess performed on a protruding structure showing charge distribution,and FIG. 8(A)-FIG. 8(C) depict example diagrams of an anodic oxidationprocess performed on a protruding structure without showing chargedistribution, in accordance with some embodiments. A mask layer 702protects a top part of the protruding structure 704. As shown in FIG.7(A), at the beginning of the anodic oxidation process, positive chargesdistributes approximately uniformly across the protruding structure. Anoxide layer is formed approximately uniformly from top to bottom of theprotruding structure, as shown in FIG. 7(A) and FIG. 8(A). An electricfield (e.g., E_(top1)) associated with a top part 706 of the protrudingstructure 704 is approximately equal to an electric field (e.g.,E_(bot1)) associated with a bottom part 708 of the protruding structure704 in magnitude. The protruding structure 704 is associated with aresistance R₁.

As shown in FIG. 7(B), further into the anodic oxidation process, thecharge distribution changes as the oxide grows. The oxide grows more atthe bottom part 708 than at the top part 706, as shown in FIG. 7(B) andFIG. 8(B). An electric field (e.g., E_(top2)) associated with the toppart 706 becomes smaller than the electric field E_(top1) in magnitude,while an electric field (e.g., E_(bot2)) associated with the bottom part708 is approximately equal to the electric field E_(bot1) in magnitude.A resistance R₂ associated with the protruding structure 704 at thisstage is larger than the resistance R₁.

At the end of the anodic oxidation process, the oxide further grows atthe bottom part of the protruding structure 704 until a conductionchannel of charges to the top part of the protruding structure 704 isclosed off, as shown in FIG. 7(C) and FIG. 8(C). An electric field(e.g., E_(top3)) associated with the top part decreases to a smallmagnitude (e.g., zero), and an electric field (e.g., E_(bot3))associated with the bottom part also becomes approximately zero. Oncethe conduction channel of charges to the top part is sealed off, theoxide stops growing at the top part. The un-oxidized semiconductormaterial (e.g., Si, GaAs, semiconductor-on-insulator, III-V materials,II-VI materials, etc.) at the top part of the protruding structure 704forms a nanowire.

FIG. 9(A)-FIG. 9(D) depict example diagrams showing anodic oxidationperformed on different wafer electrodes, in accordance with someembodiments. Different wafer electrodes include protruding structures ofdifferent widths respectively. As shown in FIG. 9(A)-9(D), underapproximately same conditions for anodic oxidation (e.g., duration ofoxidation), nanowires are formed for the protruding structures with awidth of 60 nm, where oxides surround the formed nanowires. For theprotruding structures with widths of 70 nm, 80 nm, and 90 nm, oxides didnot grow farther enough to enclose parts of the semiconductor materialto form nanowires. It indicates that under certain conditions for anodicoxidation (e.g., duration of oxidation), nanowires can be formed for aprotruding structure with a width no larger than a width threshold.

FIG. 10(A) depicts an example diagram showing a pattern of a protrudingstructure on a wafer electrode, and FIG. 10(B) depicts an examplediagram showing a cross-section view of the pattern along a cutline AA',in accordance with some embodiments. As shown in FIG. 10(A), theprotruding structure 1002 is patterned on a wafer electrode 1004 thatincludes a substrate (e.g., Si, GaAs, semiconductor-on-insulator, III-Vmaterials, II-VI materials, etc.). For example, the patterning of theprotruding structure 1002 is performed through e-beam lithography andetching. In another example, the patterning of the protruding structure1002 is performed through extreme ultraviolet lithography, resisttrimming, and etching. In yet another example, the patterning of theprotruding structure 1002 is performed through a nano-patterningprocess, e.g., charged-ion-beam (CIB). As shown in FIG. 10(B), differentprofiles of the protruding structure 1002 can be formed. The aspectratio of the protruding structure 1002 exceeds an aspect ratio threshold(e.g., 1). In some embodiments, a mask 1006 is formed throughlithography, or formed during a subsequent anodic oxidation process.

FIG. 11 depicts an example diagram showing a cross-section view of awafer electrode including a protruding structure after anodic oxidation,in accordance with some embodiments. As shown in FIG. 11, a nanowire1102 is formed in the protruding structure 1104 and is surrounded by theanodic oxide 1106 formed during the anodic oxidation.

Specifically, non-uniform electric field (e.g., due to electric fieldself-distribution as shown in FIG. 7(A)-FIG. 7(C)) in the protrudingstructure 1104 during the anodic oxidation causes non-uniform formationof the oxide 1106. For example, a width of a top part of the protrudingstructure 1104 is larger than or equal to a width of a bottom part ofthe protruding structure 1104. The anodic oxidation of the top part ofthe protruding structure 1104 ends when the oxidation of the bottom partof the protruding structure 1104 closes off a conduction channel ofcharges to the top part. In some embodiments, the protruding structure1104 may undergo alternation of anodic oxidation and etching, so thatnanowires with small sizes (e.g., 5-7 nm) covered with a dielectricmaterial (e.g., oxides) can be formed.

FIG. 12(A) and FIG. 12(B) depict example diagrams showing formation ofmultiple nanowires through anodic oxidation, in accordance with someembodiments. As shown in FIG. 12(A), a protruding structure 1202 formedon a substrate 1204 undergoes multiple (e.g., two) etching andpassivation cycles to form multiple (e.g., two) undercut features (e.g.,scalloped shapes). Anodic oxidation is performed on the substrate 1204with the protruding structure 1202.

Multiple nanowires can be formed in the protruding structure 1202, and adielectric material 1212 (e.g., oxides) surrounds the nanowires. In someembodiments, diameters of the nanowires become smaller from top tobottom of the protruding structure 1202. In certain embodiments, thediameters of the nanowires are approximately equal with properlydesigned processes (e.g., etching cycles).

As shown in FIG. 12(B), the nanowire 1206 is formed first in a top partof the protruding structure 1202, and the nanowire 1208 is then formedin a bottom part of the protruding structure 1202. One or more nano-vias1210 are also formed during the anodic oxidation. In some embodiments,the nanowire 1206 has a diameter smaller than 9 nm. In certainembodiments, the nanowire 1208 has a smaller diameter than the nanowire1206. In some embodiments, the diameters of the nanowires 1208 and 1206are approximately equal.

FIG. 13(A)-FIG. 13(C) depict other example diagrams showing formation ofmultiple nanowires through anodic oxidation, in accordance with someembodiments. As shown in FIG. 13(A), a protruding structure 1302 formedon a substrate 1304 undergoes multiple (e.g., two) etching andpassivation cycles to form multiple (e.g., two) undercut features (e.g.,scalloped shapes). A first anodic oxidation process is performed on thesubstrate 1304 with the protruding structure 1302.

As shown in FIG. 13(B), the protruding structure 1302 is partiallyoxidized to form an original oxide 1306 (e.g., SiO₂) through the firstanodic oxidation process. One or more metal materials 1308 (e.g., Hf,Al, etc.) are formed on the original oxide 1306, e.g., through atomiclayer deposition (ALD), chemical vapor deposition (CVD), plasma-enhancedatomic layer deposition (PEALD), etc. A second anodic oxidation processis performed on the substrate 1304 with the protruding structure 1302.The metal materials 1308 are converted to a high-k dielectric material(e.g., metal oxides) that is formed on the original oxide 1306.

As shown in FIG. 13(C), at the end of the second anodic oxidationprocess, nanowires 1310 and 1312 and/or nano-channels 1314 are formedand surrounded by the oxide 1318 (e.g., SiO₂) and the high-k dielectricmaterial 1316. For example, the effective dielectric constant of themixture of the high-k dielectric material 1316 and the oxide 1318 islarger than that of the oxide 1318. In some embodiments, the diametersof the nanowires 1310 and 1312 are approximately equal and smaller than9 nm. In certain embodiments, the diameter of the nanowires 1310 islarger than the diameter of the nanowire 1312. The substrate 1304includes a ridge section 1320 extending under the protruding structure1302. For example, the ridge section 1320 extends along a same directionas the nanowires 1310 and 1312.

FIG. 14(A)-FIG. 14(C) depict other example diagrams showing formation ofmultiple nanowires through anodic oxidation, in accordance with someembodiments. As shown in FIG. 14(A), a protruding structure 1402 formedon a substrate 1404 undergoes multiple (e.g., two) etching andpassivation cycles to form multiple (e.g., two) undercut features (e.g.,scalloped shapes).

As shown in FIG. 14(B), one or more metal materials 1406 (e.g., Hf, Al,etc.) are formed on the protruding structure 1402, e.g., through ALD,CVD, PEALD, etc. An anodic oxidation process is performed on thesubstrate 1404 with the protruding structure 1402 and the metalmaterials 1406. The metal materials 1406 are converted to a high-kdielectric material (e.g., metal oxides).

As shown in FIG. 14(C), at the end of the anodic oxidation process,nanowires 1410 and 1412 and/or nano-vias 1414 are formed and surroundedby a mixture 1408 of the high-k dielectric material and the anodic oxide(e.g., SiO₂). For example, the effective dielectric constant of themixture of the high-k dielectric material and the anodic oxide is largerthan that of the anodic oxide. In some embodiments, the diameters of thenanowires 1410 and 1412 are approximately equal and smaller than 9 nm.In certain embodiments, the diameter of the nanowires 1410 is largerthan the diameter of the nanowire 1412. The substrate 1404 includes aridge section 1416 extending under the protruding structure 1402. Forexample, the ridge section 1416 extends along a same direction as thenanowires 1410 and 1412.

FIG. 15 depicts an example diagram showing anodic oxidation for multiplewafer electrodes, in accordance with some embodiments. As shown in FIG.15, multiple cathode electrodes 1502 including metal materials (e.g.,Ag, Pt, etc.) and multiple anode electrode 1504 including asemiconductor wafer (e.g., Si, GaAs, semiconductor-on-insulator, III-Vmaterials, II-VI materials, etc.) are immersed in an electrolyticsolution 1506 which is contained in a tank 1514 for anodic oxidation.The cathode electrodes 1502 and the anode electrodes 1504 are connectedelectrically to one or more power supplies (not shown).

The nanowires formed through anodic oxidation as described above can beused for fabricating nanowire devices. FIG. 16 depicts an examplediagram showing a top view of an original mask for forming a protrudingstructure for a transistor structure, in accordance with someembodiments. As shown in FIG. 16, the protruding structure 1602 can bedisposed between a source region 1604 and a drain region 1606. Forexample, the patterning of the protruding structure 1602 is performedthrough e-beam lithography and etching. In another example, thepatterning of the protruding structure 1602 is performed through extremeultraviolet lithograph, resist trimming, and etching. In yet anotherexample, the patterning of the protruding structure 1602 is performedthrough a nano-patterning process, e.g., charged-ion-beam (CIB).

Anodic oxidation is performed to form one or more nanowires in theprotruding structure 1602. Cross-section views along a cutline xx', acutline yy' at W_(A), and the cutline yy' at W_(B) are shown in FIG.17(A), FIG. 17(B) and FIG. 17(C), respectively. As shown in FIG. 17(A)and FIG. 17(B), the nanowires 1702 are formed between a source structure1704 and a drain structure 1706 and surrounded by a dielectric material1708 (e.g., oxides) that is formed during the anodic oxidation.Nano-vias 1712 (e.g., filled with air or solids) are formed as well. Thesubstrate 1710 includes a semiconductor-on-insulator wafer, silicon,III-V materials, II-VI materials, etc. A cross-section view of the drainstructure 1706 is shown in FIG. 17(C). The drain structure 1706 iscontinuous to the substrate 1710, or isolated from the substrate 1710(e.g., through suitable design of anodic oxidation). A ridge section1714 extends under the protruding structure 1602 and along a samedirection as the nanowires 1702.

FIG. 18(A)-FIG. 18(D) depict example diagrams showing a process forfabricating a transistor structure using nanowires formed through anodicoxidation, in accordance with some embodiments. As shown in FIG. 18(A),an interlayer dielectric (ILD) layer 1802 is formed on the wafer.Lithography and etching are performed to open source/drain contactareas, and interconnect metallization is carried out to formsource/drain contacts 1804 and 1806, as shown in FIG. 18(B). Lithographyis performed to pattern gate contact areas, and a selective etching isperformed to remove part of the ILD layer 1802, but not the dielectricmaterial 1708, as shown in FIG. 18(C). CIB (e.g., He/Ne beam) isperformed to form multiple metal nanogate lines 1808 to form atransistor structure, as shown in FIG. 18(D).

FIG. 19(A)-FIG. 19(D) depict other example diagrams showing a processfor fabricating a transistor structure using nanowires formed throughanodic oxidation, in accordance with some embodiments. As shown in FIG.19(A), an interlayer dielectric (ILD) layer 1902 is formed on the wafer.Lithography is performed to pattern source/drain contact areas and gatecontact areas, and etching is performed to the ILD layer 1902 and theoxide 1708 in the source/drain contact areas and the gate contact areas.Interconnect metallization is carried out to form source/drain contacts1904 and 1906, as shown in FIG. 19(B). A dielectric material 1908 (e.g.,a high-k material) is formed (e.g., through CVD, ALD, PEALD, etc.) onthe wafer, as shown in FIG. 19(C). The formation of the dielectricmaterial 1908 also shrinks a gap size for nanogate formation (e.g., atrench refill process). In some embodiments, a conductive material 1910(e.g., metal-containing materials) is formed (e.g., through CVD, ALD,PEALD, etc.) on the wafer to form nanogates, as shown in FIG. 19(D). Incertain embodiments, CIB (e.g., He/Ne beam) is performed to formmultiple metal nanogate lines. Finally, the dielectric material 1908 ontop of the source/drain regions are removed.

FIG. 20 depicts an example diagram showing a nanowire device, inaccordance with some embodiments. As shown in FIG. 20, a stack ofnanowires 2002 are fabricated using anodic oxidation as described above.In some embodiments, anodic oxides surrounding the nanowires 2002 arepartially removed to physically isolate the nanowires 2002. In certainembodiments, the anodic oxides that surround the nanowires 2002 arecompletely removed to expose the nanowires 2002. Dielectric materials(e.g., high-k materials) are formed on the nanowires 2002, and CIB isperformed to form a single metal nanogate line or multiple metalnanogate lines. Source/drain contacts 2004 and 2006 are formed throughlithography, etching and contact formation. A gate-all-around transistorusing multiple nanowires is formed.

FIG. 21 depicts an example flow chart for forming nanowires, inaccordance with some embodiments. At 2102, a first protruding structureis formed on a substrate. At 2104, the first protruding structure isplaced in an electrolytic solution. At 2106, anodic oxidation isperformed using the substrate as part of an anode electrode. At 2108,one or more nanowires are formed in the protruding structure. Thenanowires are surrounded by a first dielectric material formed duringthe anodic oxidation.

The present disclosure describes formation of nanowires for devicefabrication using anodic oxidation. In some embodiments, the devices,structures and methods described herein are configured to fabricatevertically self-aligned nanowires.

According to one embodiment, a method is provided for forming nanowireson a substrate. A first protruding structure is formed on a substrate.The first protruding structure is placed in an electrolytic solution.Anodic oxidation is performed using the substrate as part of an anodeelectrode. One or more nanowires are formed in the protruding structure.The nanowires are surrounded by a first dielectric material formedduring the anodic oxidation.

According to another embodiment, a structure includes: a substrate, aprotruding structure formed on the substrate, and one or more nanowiresformed in the protruding structure. The substrate includes a ridgesection extending under the protruding structure.

According to yet another embodiment, a device includes: a source region,a drain region, and a gate structure. The source region is formed on asubstrate, and the drain region is formed on a substrate. The gatestructure includes one or more nanowires disposed between the sourceregion and the drain region. The substrate includes a ridge sectionextending under the nanowires.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method for forming nanowires on a substrate,the method comprising: forming a first protruding structure on asubstrate; placing the substrate including the first protrudingstructure in an electrolytic solution; performing anodic oxidation usingthe substrate as part of an anode electrode; and forming one or morenanowires in the protruding structure, the nanowires being surrounded bya first dielectric material formed during the anodic oxidation.
 2. Themethod of claim 1, wherein the anode electrode further includes aconductive material configured to be electrically connected to a powersupply and be in contact with the substrate.
 3. The method of claim 1,wherein: the anode electrode further includes a conductive material anda metal electrode, the metal electrode being disposed between thesubstrate and the conductive material; and the conductive material isconfigured to be electrically connected to a power supply and be incontact with the substrate and the metal electrode.
 4. The method ofclaim 1, wherein the first protruding structure includes: ananowire-shaped structure, a nanoslate, a nanorod, or a nanostructuredisposed between pads.
 5. The method of claim 1, wherein: the firstprotruding structure has a width and a height; an aspect ratio of thefirst protruding structure is equal to the height divided by the width;and the aspect ratio is larger than an aspect-ratio threshold.
 6. Themethod of claim 1, wherein the first protruding structure has a width ina range of about 10 nm to about 100 nm.
 7. The method of claim 1,wherein the first protruding structure has a height in a range of about10 nm to about 500 nm.
 8. The method of claim 1, wherein the firstprotruding structure includes a sidewall corresponding to: a verticalshape, a trapezoidal shape, a scalloped shape, or a shape of which a topwidth is larger than or equal to a bottom width.
 9. The method of claim1, wherein: the first protruding structure includes a first part and asecond part under the first part; oxidation of the first part stops whenthe second part is completely oxidized during the anodic oxidation; anda first nanowire is formed when the oxidation of the first part stops,the first nanowire corresponding to the un-oxidized first part.
 10. Themethod of claim 9, wherein: the first protruding structure includes athird part and a fourth part under the third part; oxidation of thethird part stops when the fourth part is completely oxidized during theanodic oxidation; and a second nanowire is formed when the oxidation ofthe third part stops, the second nanowire corresponding to theun-oxidized third part.
 11. The method of claim 1, wherein theperforming anodic oxidation using the substrate as part of an anodeelectrode includes: performing a first oxidation process to oxidize partof the first protruding structure using the substrate as part of theanode electrode; forming a metal material on the partially oxidizedprotruding structure; and performing a second oxidation process tooxidize the metal material and the first protruding structure using thesubstrate as part of the anode electrode.
 12. The method of claim 1,wherein the performing anodic oxidation using the substrate as part ofan anode electrode includes: forming a material on the protrudingstructure; and performing the anodic oxidation to oxidize the metalmaterial and the first protruding structure using the substrate as partof the anode electrode.
 13. The method of claim 1, wherein one or moresecond protruding structures are formed on the substrate for nanowireformation through the anodic oxidation.
 14. The method of claim 1,further comprising: removing at least part of the first dielectricmaterial; forming a gate dielectric material on the nanowires; andforming one or more gate contacts on the gate dielectric material forfabricating nanowire devices.
 15. A structure comprising: a substrate; aprotruding structure formed on the substrate; and one or more nanowiresformed in the protruding structure; wherein the substrate includes aridge section extending under the protruding structure.
 16. Thestructure of claim 15, wherein: the one or more nanowires extend along afirst direction; and the ridge section extends along the firstdirection.
 17. The structure of claim 15, wherein the protrudingstructure includes: a nanowire-shaped structure, a nanoslate, a nanorod,or a nanostructure disposed between pads.
 18. The structure of claim 15,wherein: the protruding structure has a width and a height; an aspectratio of the protruding structure is equal to the height divided by thewidth; and the aspect ratio is larger than an aspect-ratio threshold.19. The structure of claim 15, wherein the protruding structure includesa sidewall corresponding to: a vertical shape, a trapezoidal shape, ascalloped shape, or a shape of which a top width is larger than or equalto a bottom width.
 20. A device comprising: a source region formed on asubstrate; a drain region formed on a substrate; and a gate structureincluding one or more nanowires disposed between the source region andthe drain region; wherein the substrate includes a ridge sectionextending under the nanowires.